A heterogeneous body structure is a body structure that includes a plurality of different parts or different types of parts, wherein properties within one part of the body structure are different from properties of other parts of the body structure. Further, heterogeneous body structures exhibit spatial variation in the aforementioned properties. In other words, a heterogeneous body structure is in particular anisotropic.
Insertion of an instrument into a desired position within heterogeneous body structures can be difficult or impossible. The instrument can in particular be diverted from the desired and planned movement trajectory, in particular from the insertion trajectory of the instrument. This can be due to the heterogeneity and the consequent interaction, in particular mechanical interaction, between the heterogeneous tissue and the instrument.
Heterogeneous body structures occur in tumorous body structures, in particular in tumorous biological tissues, e.g., organs such as the brain or liver, for example. As can be established with the aid of elastography, for example, tumor cells are 5 to 28 times more rigid (less elastic) than healthy tissue cells. This can be measured using ultrasound elastography or MR elastography. When using instruments that are not completely rigid, such as for example a catheter, these rigid tumor regions increase the risk of the catheter not being able to reach the desired region. This can be caused by the instrument being diverted from its desired trajectory by tumor tissue, the instrument not being able to penetrate tumor tissue, or the instrument being bent or diverted such that the dispensing direction of a catheter, for example, is no longer in the planned direction. As a result, an injected drug may remain ineffective or can even cause damage at a non-planned location in healthy tissue. The same applies, for example, when using a biopsy needle that extracts samples from an incorrect region due to the needle being diverted by more rigid regions of the heterogeneous tissue. This can lead to misinterpretations in the physician's diagnosis.